In numerical analysis of the compression molding process, the discrete element method (DEM), which can evaluate the interaction between particles and microstructure, and the finite element method (FEM), which can evaluate macroscopic deformation behavior by treating the powder bed as a continuum, are widely used. However, DEM simulates particle deformation by overlapping sphere particles, hardly evaluating the particle deformation. In addition, because FEM treats the powder bed as a homogeneous continuum, it ignores the particle information. Therefore, in this study, we focused on the multi-particle finite element method (MPFEM), which combines the advantages of both DEM and FEM. In MPFEM, individual particles are divided into elements and structural analysis at the particle scale is possible. This enables us to reproduce the contact state of particles and the deformation of particles. Therefore, the purpose of this study was the numerical analysis using MPFEM for the powder compression process to investigate the internal structure of an electrode. The effect of powder properties, such as plastic deformability and particle size distribution, on the interparticle contact area and ion/electron conduction paths was investigated. LS-DYNA (2023 R1, ANSYS Inc.) was used for the MPFEM calculation. A solid electrolyte layer was simulated using particles with plastic deformability. The particle size was 0.4 mm and the mill diameter was 6 mm. The geometry was divided into tetrahedrons for calculation.
At first, we attempted to calculate the interparticle contact area by filling and compressing plastically deformable particles. The contact areas at the center of the powder bed and near the wall were analyzed. In MPFEM, the entire system was divided into a finite number of elements, and the forces and displacements acting on the nodes were calculated. To calculate the contact area between particles, we extracted the nodes where the contact force between particles acted. Since the elements of the particle were tetrahedrons, when a force was applied to three of the four nodes, the surface formed by the three nodes was defined as the contact surface. The contact area between particles was calculated by adding up the defined contact surfaces.
It was found that the number of pairs of particles in contact was greater in the center of the powder bed than that near the wall. This would be because the center of the powder bed was compressed from multiple directions while being surrounded by particles on all sides, resulting in an increase in the number of contact pairs. In addition, the average contact area was also larger near the wall than the center of the powder bed. One of the reasons for this was that the number of contact pairs was small near the wall. The standard deviation of the number distribution of the contact area between particles was almost the same for both, although we expected that the distribution would be smaller in the center of the powder bed than near the wall. One factor that contradicted our expectations was that the number of particles evaluated in this study was very small. However, we were successful in quantitatively evaluating the contact area inside the powder bed by analyzing the load generated at the nodes.
In conclusion, we succeeded in calculating the contact area between each particle during the compression process of plastic particles using MPFEM. In poster presentations, we will also introduce to our analysis of interparticle contact information between all particles and systematization of the effect of powder properties on the internal structure.